In high-frequency surgery, high-frequency currents are used for cutting and coagulating of human tissue. For cutting, an approximately continuous high-frequency current is supplied. In the process, a small arc is formed between the high-frequency surgical probe and the tissue to be cut. The high-frequency generator must deliver a voltage that is sufficient to strike the arc. The high-frequency current passing into the tissue heats the tissue adjacent to the high-frequency surgical probe so strongly that the cell sap volatilizes explosively and thus severs the tissue.
For coagulating, the high-frequency power is supplied in pulsed form. The mean supplied power is then low enough that explosive steam production no longer occurs. Instead, the cell sap escapes slowly and the tissue dries out without being severed. Under these conditions, however, the tissue acquires high electrical resistance. If a deep coagulation effect is to be achieved, the high frequency voltage must have relatively high pulse amplitudes, in order to maintain the current flow through the high-resistance surface.
For tissue cutting, a relatively high mean power is supplied to the patient. This conceals the known risks, such as burns, for example, for the patient. It is therfore very important to adjust the power of the high-frequency generator to the closest possible value. The output voltage must be so chosen that a sufficient tissue-severing effect just occurs, but that no excess power is delivered to the patient.
It is known that a manual generator adjustment during cutting always leads to unsatisfactory results. For this reason, a device for electrical tissue cutting in surgery is described in German Patent 2,5504,280, in which device the instantaneous condition of the cutting process is monitored by means of electrical signals. The output voltage is so adjusted with a control device that the cutting process is controlled in constant manner to a desired condition. In one embodiment, the intensity of the arc burning between the surgical probe and the tissue is measured and controlled in constant manner for this purpose. This arc control provides a significant reduction of the mean power supplied to the patient as compared with manually adjustable high-frequency generators.